How scientists study Earth's geocorona, the farthest portion of the planet's exosphere

Learn about the sun's corona, which is nonlethal despite a temperature of millions of degrees

The outermost layer of the sun's atmosphere is best seen during a solar eclipse, when the moon blocks the much brighter (and significantly cooler) solar surface. Despite the high-energy particles in the corona moving fast enough to escape the sun's gravity and gradually become solar wind, their density is too low to contribute meaningfully to the region's overall radiation.

Why the edge of Earth's atmosphere varies depending on which property is considered

As the distance from Earth's center increases, the planet's gravitational force weakens, causing it to gradually lose its ability to retain gases at the farthest edge of its atmosphere—the exosphere. At a height of approximately 200,000 kilometers (124,000 miles)—halfway to the Moon—the exosphere has so little density that it is indistinguishable from interstellar space.

In 2025, the European Space Agency created the first artificial solar eclipse in space when one spacecraft cast a shadow onto another spacecraft to enable observations of the sun's outermost atmosphere.

Understanding why charged particles from the sun protect Earth from more dangerous particles

The solar wind engulfs the solar system in a protective bubble called the heliosphere, which was first theorized in the late 1950s based on studies of cosmic rays—high-energy particles traveling through space at near light speed. The heliosphere shields the solar system from much of this ionizing radiation originating elsewhere in the Milky Way.

How do scientists study far away stars?

Astronomy is the only science that is purely observational: meaning, scientists can't study stars in a lab. Here's a breakdown of how modern researchers use new tools to understand objects billions of light years away. As it turns out, the rules of science allow us to identify, categorize, and experiment with phenomena light years away.

Scientists can map Earth's shape and structure by measuring the ratios of certain particles arriving from different directions in space, as these ratios change with the density of the material particles travel through.

Solar eclipses block the sun enough to enable scientists to observe its faint outer atmosphere, or corona, whose spectrum led to the discovery of helium over a decade before it was identified on Earth.

The Oort cloud, our solar system's theoretical icy shell

Recurring comets lead astronomers to believe they originate from an extremely distant, icy shell encapsulating the solar system. They call it the "Oort cloud," and this giant swarm of icy objects is as fascinating as it is is massive. Home of comets and a tremendous number of planetesimals, this NASA site introduces you to the Oort.

Scientists investigate Earth's interior by studying seismic waves

Scientists investigate Earth's interior by studying seismic wavesBelow Earth's atmosphere lies the crust, which extends to the Mohorovičić discontinuity between five and 20 miles below Earth's surface. Below the crust lies the mantle, the liquid-metal outer core, and the solid inner core, which surpasses 5,200 degrees Celsius (9,392 degrees Fahrenheit).

Zooming out from Earth to the edge of space

For perspective on the universe's absolute massiveness, watch this four-minute video. Beginning at a facility in Germany, the "camera" pulls back revealing the surrounding countryside, Germany itself, Europe, the Earth, and so on. At one point stars form galaxies and galaxies, at a distance, become as seemingly "small" as the individual stars.

View the transparency of Earth's atmosphere and how it blocks most forms of light

The gases that make up Earth's atmosphere block most harmful forms of electromagnetic radiation from reaching the planet's surface, except for some ultraviolet light. Their transparency to radio waves means this form of light can reach Earth's surface, which is why most radio telescopes are ground-based rather than space-based.

Evidence for a ninth planet in our solar system

Is there a massive ninth planet on the edge of our solar system? Many of our solar system's most distant objects tend to swing out in one direction, hinting at evidence for a previously unknown ninth planet potentially larger than Earth. This theoretical planet's orbital period is estimated to be roughly 20,000 years, revolving around the sun at a distance of 60 billion miles. Experts break down the evidence in this quick video.

Although no such planet exists in our solar system, the most common subtype of exoplanet in the galaxy is the sub-Neptune world, which is larger than Earth but smaller than the ice giants.

Explore how far you've traveled through space while living on Earth

Using the "Cosmic Odometer," users can enter their birthday and learn how far they have moved through space due to the combined effects of Earth's rotation around its axis, the planet's orbit around the sun, the solar system's trajectory through the Milky Way, and the galaxy's motion through the universe.

An exoplanet detection method involves measuring a host star's auroras

Astronomers have reported indirectly identifying a planet by observing its debris interacting with the magnetic field of the star it orbits. The interaction is a larger-scale version of the auroras observed on Jupiter, which are produced when material released by its moon, Io, interacts with the gas giant's magnetic field.

View a diagram of Earth's atmosphere, which is composed of five layers

Starting from the surface, the troposphere is home to Earth's weather, followed by the stratosphere, which houses the ozone layer, and the mesosphere, which burns up most debris from space. Above these layers lies the thermosphere, where auroras are produced, and the exosphere, which lacks a clear outer boundary as it fades into outer space.

By separating light with tools such as prisms, scientists can reveal the presence and composition of celestial matter by identifying color fingerprints unique to specific elements and molecules.

The history of helioseismology, which studies seismic waves traveling within the sun

Following World War II, scientists began studying the sun's influence on radio waves, the most popular form of mass communication at the time. NASA missions to study the sun's interior have since helped develop explanations for various phenomena in its atmosphere and protect digital infrastructure.

Asteroids are often unobserved until they are days away from Earth

Even those large enough to cause local or regional damage are too small, dim, and far away to be observed readily from cosmological distances. New tools, like NASA's NEO Surveyor telescope, aim to address gaps in detection systems.

Solar eclipses are a cosmic coincidence because the moon is 400 times smaller than the sun but about 400 times closer to Earth, allowing it to block sunlight for those on Earth within its shadow.

Earth's magnetic field can trap high-energy charged particles produced by the sun and distant cosmic events in doughnut-shaped rings called Van Allen belts.

As seen in the dark region of the Horsehead Nebula, clouds of space dust can block some forms of light from reaching telescopes, impairing observations and data collection.

The impacts of the solar maximum on Earth, from telecommunications to auroras

During the peak of the sun's 11-year cycle, plasma emissions stronger than the average stream of particles from the sun can compress and distort the Earth's magnetic field, allowing auroras to be seen farther from the poles. Distortions in the ionized layer of Earth's atmosphere can also alter the path of communication transmissions through the air. (Some readers may experience a paywall.)

How we know what's deep inside the Earth, despite never traveling there

We'll likely never see the Earth's core, but we can make educated guesses about what it's like down there. Nearly as hot as the sun's surface and under impossibly high pressure, the inner Earths extreme conditions make it impossible to explore. Yet, seismic waves during earthquakes, volcanic eruptions, and light waves from the sun provide fascinating insights about our planet's mantle, crust, and core.

The best location to view auroras is within the auroral oval

Earth's magnetic field pushes trapped particles from the solar wind toward the planet's magnetic poles, where they can descend and collide with atmospheric gases in a ring located between 60 and 75 degrees of latitude. Auroras can also be viewed at lower latitudes—the sub-auroral oval and solar storm zones—if the sun produces powerful solar storms.

Breaking down the ionosphere, which reflects radio waves from Earth's surface

Made up of ionized regions within the mesosphere and thermosphere, the ionosphere contains charged particles produced when solar radiation knocks electrons free from atoms and molecules in the atmosphere. Before satellites, radio operators would bounce signals off these regions to wrap around the planet and extend the range of transmissions.

One of the hottest known exoplanets seems to snow an active ingredient of sunscreen, titanium dioxide—but only on the dark side of the planet.

Scientists quantify how far from the poles auroras will be visible using the G-scale

The Geomagnetic Storm scale indicates the expected severity of the deformation of Earth's magnetic field based on the amount of energy injected by the solar wind. Solar activity is monitored using various satellites to forecast these storms, which can also be used to anticipate damage and disruption to power systems, radio communications, and satellite navigation.

The sun emits a continuous stream of plasma known as the solar wind

Composed of charged particles—electrons and ions—the solar wind is deflected around the Earth by the planet's magnetic field. More powerful solar storms, known as coronal mass ejections, are short-lived but produce huge clouds of plasma that disrupt technology upon reaching Earth.

NASA explores Earth's deepest oceans to prepare for space

By studying extreme environments in Earth's hadal zone—the deepest part of the ocean —NASA tests technologies, probes life under crushing pressure, and gathers clues about potential oceans and possible life on worlds like Europa and Enceladus.

Explaining the galaxy-sized gas bubbles hovering around the Milky Way

Depth perception is hard to achieve when looking out into space. For decades, two camps of astrophysicists have disagreed over the nature of the North Polar Spur, a radio-wave emitting arc above the Milky Way galaxy's plane. Was it close and relatively small? Or was it faraway and much more massive? New research utilizing X-ray mapping of the galaxy has helped clarify the existence of both so-called smaller Fermi bubbles and larger X-ray ones.

See to the edge of the universe with this two-decade astronomy project

A New Mexico telescope has captured astronomical data for two decades to compile this map of the universe. Starting from earth and ending at the "edge" of the universe, it shows one slice of the cosmos: a total of 200,000 galaxies.

The Earth orbits the sun within the Orion Spur arm of the Milky Way galaxy

The solar system is roughly halfway between the galaxy's outer rim and its center, which is located about 25,000 light years away. The Milky Way is itself one of hundreds of thousands of galaxies in the Virgo Supercluster.

Neptune is the farthest planet from the sun, orbiting 30 times farther than Earth and taking 165 years to complete one revolution.

The importance of the mesosphere, the coldest part of Earth's atmosphere

Atmospheric gases are dense enough in this region to begin burning up debris traveling toward Earth's surface, producing meteor showers, or shooting stars. Although we normally associate decreasing temperatures with increasing altitude, temperatures increase beyond the mesosphere layer due to the absorption of high-energy ultraviolet radiation and X-rays.

Coronal mass ejections and solar flares produce the most extensive auroras

The most intense geomagnetic storms are produced when massive clouds of plasma—ionized gas—are expelled from the sun's upper atmosphere and interact with the Earth's magnetic field. These storms expand where auroras are bright enough to be seen to regions farther from the poles, particularly during peak periods of the sun's 11-year intensity cycle.

View a colorful gallery of solar features, including coronal loops and filamentary prominences, curated by the National Solar Observatory.

View historical records of solar observations and discoveries, from telescopes in the early 1600s revealing sunspots to NASA's Parker Solar Probe photographing the sun from within its outer corona in 2025.

A composite of telescope images of the sun, which each reveal unique solar features

While traditional cameras can reveal sunspots—cooler regions on the sun's surface—in visible light, x-ray detectors can highlight explosions of high-energy plasma and magnetic fields known as coronal mass ejections. Hydrogen-alpha filters can reveal clouds and filaments of material suspended in magnetic fields above the sun's surface.

As of 2025, humans have only dug 0.2% the way to Earth's center

The Kola Superdeep Borehole revealed two billion-year-old fossils and underground water, but the immense temperature and pressure prevented further tunneling. Beyond those depths, scientists know of Earth's interior by analyzing how seismic waves move.

In 1997, the Compton Gamma Ray Observatory identified 'positron geysers'—fountains of antimatter particles—emerging from near the center of the Milky Way.

The edge of the Milky Way may be identified by its star-forming disk

Like Earth's atmosphere and its core, galaxies become more diffuse with increasing distance from their centers, making it hard to define where they end. However, one approach focuses on where gas concentrations are no longer dense enough to support measurable star formation.

Earth is the only terrestrial planet with a magnetic field

Its magnetosphere emerges from a complex interior process of electrical conduction, heat, and motion known as the geodynamo. The magnetic field shields the Earth from unsafe cosmic radiation, providing one of the many conditions required for life.

The Hubble Space Telescope made discoveries within our solar system and across the universe

The observatory helped confirm the presence of water on Jupiter's moon Europa, and uncovered seasonal variations on planets like Uranus. It also observed exoplanets and gravitational lensing, proved the existence of supermassive black holes at the centers of galaxies, and detected the accelerated expansion of the universe.

The Oort Cloud is a shell of icy objects surrounding the solar system, from which many comets originate

Proposed in 1950 by Jan Oort, the theoretical structure is believed to be the origin of comets with periods of more than 200 years. Leftover planetary building blocks from the early solar system formed the Oort Cloud after being flung out by the gravity of planets like Jupiter.

From the stellar core to the surface, the sun's density decreases from more than 10 times that of lead to 0.00001% that of air.

From the stellar core to the surface, the sun's density decreases from more than 10 times that of lead to 0.00001% that of air, while temperatures drop from millions to thousands.

Comets serve as time capsules of the early solar system

The frozen objects preserve the molecular composition of the solar system's formation, dating back about 4.6 billion years. Spectral analysis of the gases they release when heated upon approaching the sun in eccentric orbits reveals this composition and helps assess solar system formation models.

The geoid depicts what Earth would look like if not for tides and currents, given the planet's rotation and uneven gravitational field.

First-ever image of the sun's south pole

For the first time, we have clear images of the sun's mysterious south pole. Captured in March 2025, by ESA and NASA's Solar Orbiter, this footage reveals magnetic chaos that could unlock answers about solar storms, the sun's strange 11-year cycle, and why its atmosphere is hotter than its surface.

Because the half of Earth that faces the sun is larger than the area of the shadow cast by the moon during a solar eclipse, observers may experience a total, annular, or partial eclipse.